1. Field of the Invention
This invention relates to surface finish smoothness measurements and in particular to apparatus for continuously measuring the smoothness of a moving sheet or web of material and comparing the resulting smoothness measurements to a reference standard, with means to automatically compensate for environmental conditions and contaminants. 2. Prior Art
In papermaking, smoothness is the characteristic of the paper's surface which is primarily responsible for the paper's capability to produce, among other uses, the uniformity of print density of a solid or full tone print, when the paper or plastic sheet is used in newsprint, periodicals, catalogs, flexible packaging displays, etc.
Numerous methods have been proposed and used for surface finish measurements of smoothness, mostly laboratory methods based on the air leak principle. The instruments presently used are not adaptable for continuous on-machine monitoring for various reasons, principally because of the slow response of an air column, non-linear readout, and other restrictions which limit the method to laboratory sampling techniques.